Contact-transfer electrostatic printing system

ABSTRACT

A system and method for electrostatic printing in which an electrostatic latent image charge configuration is established on the non-conducting surface of a transfer medium and developed with a liquid toner suspension in the form of toner marking particles suspended in a fluid. The liquid from the liquid toner suspension applied to the transfer medium is removed leaving toner particles electrostatically retained against the surface of the transfer medium in accordance with the electrostatic latent image charge configuration. A print receiving medium is compressed or pressure biased by means of a roller or other means having a surface preferably resilient against the transfer medium and the compressed print receiving medium and deposited toner particles are contact heated by the pressure roller or means in the transfer area so that toner particles are melted and fixed to the print receiving medium in the configuration of the electrostatic latent image.

Unite States ate L1 [191 Blake 51 May'2l, 1974 CONTACT-TRANSFER ELECTROSTATIC PRINTING SYSTEM 1 [75] Inventor: David E. Blake, Woodside, Calif.

[73] Assignee: Electroprint, Inc, Palo Alto, Calif.

22 Filed: Jan. 21,197: 211 App]. No.: 219,616

52 use! ..355/3R,96/l.4,117/21,

[51] Int. Cl. G031) 15/00 [58] Field of Search 355/3 R, 10; 96/14; 1 17/175, 21

['56] References Cited UNITED STATES PATENTS 3,698,314 10/1972 Grier 1.17/21 3,284,224 1l/1966 Lehmann 355/10 X 3,669,706 6/1972 2 Sanders et a1. 117/21 3/1972 'lressman et a1 355/3 Primary Examiner-Richard L. Moses Attorney, Agent, or Firm-Townsend and Townsend [57] ABSTRACT A system and method for electrostatic printing in which an electrostatic latent image charge configuration is established on the non-conducting surface of a transfer medium and developed with a liquid toner suspension in the form of toner marking particles suspended in a fluid. The liquid from the liquid toner suspension applied to the transfer medium is removed leaving toner particles electrostatically retained against the surface of the transfer medium in accordance with the electrostatic latent image charge configuration. A print receiving medium is compressed or pressure biased by means of a roller or other means having a surface preferably resilient against the transfer medium and the compressed print receiving medium and deposited toner particles are contact heated by the pressure roller or means in the transfer area so that toner particles are melted and fixed to the print receiving medium in the configuration of the electrostatic latent image.

38 Claims, 11 Drawing Figures PATENTEDHAYZ m4 3,811,765

SHEET 1 OF 2 This invention relates to a new and improved electrostatic printing system and method and in particular to an electrostatic contact transfer printeror copier for I electrostatic printing on plain untreated paper and a variety of other untreated surfaces using liquid toner marking material.

By providing a system and method for electrostatic printing with liquid toners, the present invention avoids the inherent difficulties in handling, confining, and conveying dry toners and the unreliability of triboelectric dry particle charging due to variation with atmospheric conditions. Liquid toners, which utilize a different charging method than dry toner particles, are less subject to changes in ambient conditions. Furthermore, the use of liquid toners in combination with the contact transfer process of the present invention permit direct printing or untreated paper and other surfacesand fixing of toner marking material to the paper, print receiving medium, or other copy surface with much less heat than that required for dry toner particles in conventional electrostatic copiers. Thus, the present invention combines the advantages of liquid toner marking material with the capability of printing on untreated, plain paper or any other print receiving medium or substrate.

The present invention generally contemplates providing a transfer medium formed with a dielectric surface and means for establishing an electrostatic latent image on the dielectricsurface of the transfer medium. The electrostatic latent image is developed at a developing station which applies to the surface of the transfer medium a liquid toner suspension marking material preferably in the form of toner marking particles suspended in a liquid and the liquid is thereafter removed leaving substantially or nearly dry toner particles on the transfer medium surface in the charge configuration of the electrostatic latent charge image.

The invention also contemplates providing a transfer and fixing station at which the developed image on the transfer. medium is transferred under heat and pressure to a print receiving medium or substrate such as paper. The print receiving medium or substrate is compressed or pressure biased against'the surface of the transfer medium at the same time that heat is applied to the print receiving mediumand toner particles so that the toner is melted and fixed to the print receiving medium.

In one embodiment, the transfer medium is formed in the configuration of a transfer drum formed with an insulative or dielectric outer surface. An imaging station is provided for establishing on the dielectric surface of the drum an electrostatic latent image during rotation of the drum. At the developing station, a liquid face of the roller is maintained at a high temperature sufiicient to melt the toner particles. The printreceiving medium is fed between the roller and the transfer drum and the roller is compressed or pressure biased against the surface of the drum. The toner markingparticles on the transfer drum. surface are thereby melted and fixed to the transfer medium in the configuration of the electrostatic latent image.

While the pressure roller need not be formed with a surface of rubber or other elastomeric material and can, in fact, be formed with a solid surface, a feature and advantage of the rubber or other elastomer surface is that the elastomer cushions the contact between the hot roller and transfer drum and furthermore, because of the deformation of the elastomer, increases the transfer area and, therefore, the length of time available for melting and transferring the toner particles to the print receiving medium. The increased transfer area and increased time of fixing tends to compensate for any irregularity of the paper or print receiving medium'and the dielectric coated transfer drum. A potenage.

. fer medium surface in the configuration A variety of electrostatic latent imaging stations for establishing on the dielectric surface 'of the transfer drum or other transfer medium an electrostatic charge image configuration is provided by the present invention. Thus, an ion corona source such as a line corona source is provided spaced from the transfer drum or other transfer medium surface. The transfer drum is rotated or the transfer medium is translated relative to the actuated line corona source and resultant ion stream whichis directed towardthe transfer medium surface. In one form. of the invention, a twodimensional screen is interposed between the ion source and transfer medium surface and is translated in ductive layer for supporting a double-layer charge electrostatic latent image across the surface of the screen providing fringing fields of force withinthe apertures of the screen of selected orientations and strengths for selectively blocking and enhancing the flow of ions or other charge particles directed through the apertures of the screen from the line corona source. The stream of ions is thereby selectively controlled over a continuous range providing continuous grey-scale control and the ions or other charge particles are thereby selectively deposited on the transfer drum surface or other transof the image to be reproduced.

A double layer charge electrostatic latent image can be established on the modulating apertured screen at an optical imaging station by first initially charging the screen to provide a uniform double layer charge on either side of the insulative layer of the screen and thereafter selectively dissipating the charges across the screen in accordance with the relative intensities of an image projected on the screen. In this arrangement, the insulative layer of the screen consists of a photoconductive insulating material.

In one alternative form of the electrostatic latent imaging station, a stationary ion flow or charged particle flow screen modulator is interposed between the ion source and transfer medium surface. The stationary modulator consists of a multi-layered bar of an insulative layer with a continuous conductive layer formed on one side and a segmentedconductive layer formed on the other side. At least one row of apertures is formed through the bar so that a segment of the segmented conductive layer substantially surrounds one of the apertures and sothat each aperture is separately electrically addressable through the conductive segments while a selected fixed potential is applied to the continuous conductive layer on the other side for controlling the flow of ionsor other charged particles directed through the apertures of the screen to deposit charges on the dielectric surface of the transfer medium in a desired configuration.

A variety of other imaging stations can be provided for establishing an electrostatic latent image directly on the transfer mediumsurface including conventional xerographic imaging stations.

The invention further contemplates the provision of unique liquid toners in the electrostatic printing system and method. For the various liquid toners, the invention thus contemplates a liquid toner suspension in which dry xerographic toner particles are suspended in a resistive'carrier fluid. The dry toner particles are of the type consisting of a resin matrix containing pigment particles, dyes and other chemicals. Theseparticles are suspended in the carrier liquid, and various charge control agents can also be added to the suspension to modify the electrophoretic mobility characteristics of the particles. Preferably, toner particles with average particle size from one micron to thirty microns are used. A suspending liquid that does not appreciably attack or soften the resin matrix of the particles is used, for example, an aliphatic hydrocarbon liquid or a fluorocarbon liquid, and the resin matrix of the toner particles is selected to have a low melting point.

' While the present invention is described herein primarily with reference to its advantages in printing on plain bond and untreated paper, the systems and methods of the present invention are applicable of course for printing or copying on any print receiving medium or substrate including cloth, metal foil, plastic films, wood, and generally any smooth material.

Other objects, features and advantages of the present invention will become apparent in the following specification and accompanying drawings.

FIGS. 1A through 1D diagrammatically illustrate th essential steps of the process contemplatedby the present invention;

FIG. 2 is a diagrammatic side view of an electrostatic printing system according to the present invention;

FIG. 3 is a diagrammatic side view of another electrostatic printing system showing an alternative form of an electrocstatic latent imaging station;

' FIG. 3A is a detailed, fragmentary plan view of the imaging station;

FIGS. 4 and 4A are a fragmentary, plan view and side cross-sectional view, respectively, of the multilayered bar modulator for modulating the stream of ions originating from a line corona source; and

FIGS. 5 and 5A are a diagrammatic side view and plan view, respectively, of an alternate electrostatic latent imaging'station using a wire line corona source.

The general system and method contemplated by the present invention for printing on plain, untreated paper or other print receiving medium while maintaining the advantages of using a liquid toner are illustrated diagrammatically in FIGS. 1A through D. In FIG. 1A, the transfer medium in the form of a transfer plate 10 is formed by a base 11 coated with a layer 12 of dielectric material. An electrostatic latent image in the form of a configuration of charges 13 is established on the dielectric layer 12 by conventional xerographic techniques or other electrostatic latent imaging methods specifically contemplated by the present invention and hereinafter more fully described. The charges are illustrated as positive, but may be either positive or negative. The plate 11 is typically metal although any conductive material can be used. The dielectric coating 12 may be of any non-conducting material. Preferably, the dielectric material is hard and durable with a high dielectric constant, for example, a high PbO-content glass.

As shown in FIG. 1B, the latent charge image formed on the dielectric, layer 12 is developed using a special liquid toner consisting of relatively large particles of toner material such as particles. of a resin matrix with carbon black or other colorant in the resin matrix, which'particles are suspended in a non-conductive liquid. The characteristics of the unique toner of the present invention are described more fully hereinafter. In the process contemplated by the present invention, the ultimate transfer and fixing of the developed latent charge image involves the dry toner particles. To this end, the liquid carrier of the suspension which wets the dielectric layer is substantially removed. Advantages to removing the liquid include less liquid carrier transferred to the transfer medium, less heat required for transfer, fewer carrier vapors generated by evaporation of the liquid carrier, and more precise and controllable transfer of the dry toner particles. According-to one method for removing the liquid, an air knife 18 is provided which by means of an air jet blows off the liquid leaving the solid toner particles electrostatically retained againstthe dielectric surface 12 undisturbed. For the air jet, saturated air is preferably used to minimize vaporization of the carrier fluid which is collected after being blown off for reuse. Other techniques such as absorbent rollers and driers can be used to remove the liquid. Thus, FIG. 18 represents the toning or developing and liquid removal steps showing the solid toner particles 14 retained in position in the configuration of the latent charge image after the removal of the liquid.

FIG. 1C represents the transfer step according to which a transfer medium such as a piece of plain, untreated paper 15 is fed or placed in position directly over or adjacent the developed or toned image and a heated roller 16 is rolled across the transfer plate 10 and print receiving medium 15 between which the toner particles 14 of the developed latent charge image are sandwiched. The heated roller 16 rolls under pressure across the sandwich melting the toner and causing it to stick in the fonn of an image 17 to the transfer sheet or other print receiving medium 15. Because heat is transferred from the heated roller through the paper, the toner nearest the paper is completely melted, and flows into and. adheres tenaciously to the paper fibers. Toner particles adjacent to the transfer plate are not melted or are incompletely melted, and therefore do not adhere to the transfer plate. ln the final step, FlG. 1D, the finished copy bearing the desired toner image 17 which has been transferred and fixed is removed from the transfer plate 11). The dielectric surface 12 of the transfer plate 111 is then cleaned of the small amount of toner particles remaining. Any remaining latent charge is also removed,- for example, by wiping with alcohol or acetone, by exposure to AC corona, or exposure to DC corona of opposite sign to the remaining latent image charge. The transfer plate is then ready for reuse.

A continuous electrostatic printer or copier embodying the system and method of the present invention-is illustrated in FIG. 2. As shown in FlG. 2, the automatic copying apparatus is in the starting position for a copying or printing cycle with the heated pressure roller 30 withdrawn or disengaged from the transfer drum, and the modulated aperture electrostatic printing screen 42 for electrostatic latent imaging onto the transfer drum 31 is in raised position as hereinafter more fully described. While the hot roller 30 can be formed with a rigid solid surface, preferably a layer 32 of rubber or other elastomeric material is provided around the sur face of the drum for cushioning the shock of engagement between the surfaces of the roller 30 and drum 31 and to increase the surface contact area between the roller 30 and drum 31 because of the deformation of the elastomeric layer 32. This increase in surface area contact increases the length of time for melting and transferring toner deposited on the surface of drum 31 onto a print receiving medium sandwiched between the roller and drum. The transfer drum 31 is coated with alayer 33v of dielectric material for retaining a latent image charge configuration established on the dielectric layer at the imaging stationhereinafter more fully described. A release agent such as a silicone can also be applied to the transfer drum surface to improve removability of toner particles and marking material. The heated roller 30 and transfer drum 31' are rotated, respectively, in the direction of the arrows by motors (not shown) so that the surface velocities are identical.

On-the side of drum 31 opposite roller 30 an ion corona source 34 is provided for directing a stream of ions toward the dielectric surface 33 of transfer drum 31. To this end, a back electrode is provided on the inside of the drum either in the form of a stationary electrode to which a fixed potential is applied or in the form of a conductive inner surface 39 of the drum to which the fixed potential is applied by means of brushes during rotation of the drum. The corona source 34 in this example is formed by a wire 35 parallel with the axis of rotation of the transfer drum to provide a line source of ions and a line stream in the direction of the dielectric surface 33.

The ion stream directed towards dielectric surface 33 is selectively modulated during rotation of the drum by means of a two-dimensional multilayered apertured screen 42 which supports a double layer charge electrostatic latent image. The screen 42 includes at least a conductive layer 36 and a photoconductive insulating layer 37. At optical imaging station 38 offset from the roller axis this double layer charge latent image intended to be reproduced is established. According to one method, the photoconductive insulating layer 37 is initially uniformly charge over one side by means of, for example, a corona spray. A fixed potential applied to conductive layer 36 results in an equal and opposite charge layer being attracted to the other side of photoconductive insulating layer 37 so that a uniform double layer charge of equal and opposite charges is established across the face of the screen. This initially uniform double layer charge is selectively dissipated or equalized by means of an optical image projected onto the photoconductive layer 37 via lens 40 rendering the photoconductive layer selectively conductive in proportion to the intensity of light striking the layer permitting the charge selectively to leak away through the conductive layer 36 or selectively to equalize with the potential of the conductive layer 36 so that the double layer charge latent electrostatic image configuration is established. A variety of other screen constructions and configurations and other charging and electrostatic latent image forrning arrangements and methods are described in further detail in US. Pat. application, Ser. No. 776,146, entitled Apparatus For Aperture Controlled Electrostatic lmage Reproduction Or Constitution, now US. Pat. No. 3,647,291,-assigned to the assignee of the present case. .As a result of the double charge layers established across the screen, internal fringing fields of forceare established within the apertures 41 of the screen of selected strength and orientation for precisely controlling passage of ions. or other charge particles directed through the apertures of the screen by blocking the flow, enhancing the flow, and controlling theflow over a continuous range providing substantially continuous grey-scale control.

While the optical imaging station 38 has been described with reference to the multilayered apertured screen techniques described in the above referenced patent application, conventional xerographic and electrostatic imaging techniques can obviously be used to establish the electrostatic latent image on the dielectric surface 'of drum 31.

After the screen 42 has been prepared and imaged, it is transported downward at the same velocity as the dielectric surface 33 of drum 31 as the drum rotates. The ion'projection corona source wire 35 is then energized while the screen passes between the ion source and the drum causing an image-wise charge deposition on the dielectric surface 33.

As the drum continues to rotate, the resulting latent charge image is carried into the development unit 43 where the liquid'toner suspension is deposited on the latent chargeirnage in accordance with well known techniques, and past the air knife 44 where excess toner liquid carrier is blown back into the development unit 43 leaving substantially dry toner particles on drum surface 33. Fresh toner is brought in through inlet 45 and the depleted toner liquid partially depleted of the toner particles carried in the liquid is removed through toner outlet 46 toa tank (not shown) where the liquid is regenerated by addition of more toner particles. By using saturated air in the air knife, vaporization of the liquid carrier is minimized.

The dry or substantially dry toner particles electrostatically adhering to the dielectric surface 33 in the configuration of the image to be transferred is carried toward the hot roller transfer zone 47. When the leading edge of the toned developed image has reached a predetermined position, the solenoid 50 is actuated which drives the heated roller 30 against a piece of paper 51 previously positioned between the roller 30 and drum 31 on the paper feed chute 52. The elastomeric surface 32 of roller 30 is compressed against the dielectric surface 33 of drum 31 with the paper sandwiched in between and the toner is melted by the heat originating from roller32 and conducted through the paper so that the toner adheres to and is transferred to the paper 51. An electric field can be applied across the transfer drum and roller to assist transfer of marking material to the paper-or other print receiving medium. Because of the synchronized movements of the roller 30 and drum 31, there is'no relative motion between the roller, paper and drum in the transfer zone 47 so that smearing and distortion of the transferred image is avoided. After the last part of the paper 51 with the transferred image has passed the transfer zoner 47, the solenoid 50 is deactivated permitting the return spring 53 to retract the hot roller 30 from contact with the dielectric coated drum 31. Application of excessive heat to the drum is thereby prevented.

' A short distance beyond the transfer zone 47 a copy removal chute 54 is provided for'removing the toned copy paper 51 from the dielectric coated drum 31. Most of the toner applied in development of the elec trostatic latent image is transferred to the copy paper 51 and fused during the transfer process. The small amount of toner remaining on the drum, typically less than percent of the initial amount, is not fused and this powdery toner remainder is easily removed by cleaning roller 55. Any charge remaining from the latent charge image on the dielectric surface 33 is removed by the discharging corona 56 so that the dielectric surface 33 is fully prepared for receiving another charge image at the imaging station. Alternatively, or in addition, a roll of treated fabric can be applied against the drum surface for both charge removal and cleaning.

While the temperature of roller 30 depends to some extent upon the toner used and the speed of operation of the copier, a roller temperature of between 200F and 600F has been found satisfactory. A pressure between the heated roller 30 and drum 31 of between 2 pounds per lineal inch and 100 pounds per lineal inch can be used in the transfer, the range in pressure depending on the smoothness and heat conductivity of the. paper or-other print receiving medium used.

While the electrostatic printing and copier system of FIG. 2 has been described with reference to the use of a dielectric coated transfer drum 31 for the transfer surface, it is alsopossible to use a photoconductive surface for the transfer drum or other transfer medium. A photoconductive material for such a'photoconductive surface might'be, for example, amorphous selenium doped with arsenic or tellurium. With a photoconductive surface, conventional xerographic and electrostatic imaging techniques can be used for directly charging the drum surface. A disadvantage of the use of photoconductive materials for the surface of drum 31, however, is that photoconductors tend to be of soft and fragile materials easily damaged by abrasion and subject to heat damage. Thus, a tough, durable, dielectric coated surface is preferred.

The desirable characteristics for the dielectric surface include durability, smoothness, good toner release, and ahigh dielectric constant. A high dielectric constant material accommodates a thicker coating of toner without an initial excessive voltage or potential accumulation in the electrostatic latent image. Furthermore, with a high dielectric constant material for the transfer surface, the image holding forces retaining the toner particles against the transfer surface are increased, reducing any tendency for disruption of the toned image during the liquid removal step. On the other hand, the dielectric constant should not be so high as to interfere in the transfer step. As an example of a satisfactory dielectric coating material for the transfer drum 31, a steel drum can be coated uniformly to a thickness of 42 microns with a high PbO-content glass. The glass is selected with a dielectric constant of 18 yielding a smooth and durable image copy. With these materials and parameters, a substantially linear high velocity jet such as an air knife or other air jet sufficient to remove excess liquid does not disturb the toner particles retained against the transfer surface and the release of toner to the plain paper during transfer and fixing exceeds 95 percent.

A continuous electrostatic printer or copier using another type of electrostatic latent imaging station is illustrated diagrammatically in FIG. 3. Except for the imaging station the printer or copier is essentially the same as that illustrated in FIG. 2 and corresponding elements are numbered the same. The electrostatic latent imaging station 60 incorporated in the system of FIG. 3 is of the type described in US. Pat. application, Ser. No. 864,022 entitled Electrostatic Line Printer, now US. Pat. No. 3,689,935 and assigned to' the assignee of the present case. As shown in FIGS. 3, 3A, 4 and 4A the latent charge image configuration is established on the dielectric surface 33 of transfer drum 31 by means of a multilayered apertured modulator 61 formed by a central layer 62 of insulative material coated on one side with a substantially continuous conductive layer 63 and on the other side by a segmented layer 64. A row of apertures 65 is formed through the multilayered elements so that each segment 66 of the segmented conductive layer 64 surrounds an aperture 65. Each of the conductive segments 66 of the segmented conductive layer is insulativelyisolated from every other segment and terminates in a terminal 67 for separately electrically addressing the segments of the segmented conductive layer.

The multilayered apertures line or bar modulator 61 is aligned adjacent the surface 33 of the transfer drum 31 substantially parallel with the axis of rotation of the drum and a row of point corona sources 68 is provided along the side of the modulator opposite the drum. Each of the point corona sources 68 is substantially in line with one of the apertures 65 and the ion sources 68 direct a line or row stream of ions through the apertures of the line modulator in the direction of the back electrode 39 which may be, for example, the metal base of drum 31. The line or row stream of ions directed through the line or row of apertures of the modulator is selectively modulated in its cross-sectional flow density according to the sequence of selected signals switched and applied to the terminals 67 of the segmented layer. At the same time a constant potential is applied to the continuous conductive layer 63 so that fringing fields of force are established within the apertures between the continuous conductive layer 63 and the segment of the segmented conductive layer 64. The lines of force established within the apertures of the bar or line modulator are of selected orientations and 9 strengths for continuous grey-scale control over the latent electrostatic image charge configuration deposited on the dielectric surface 33 of the transfer drum 31.

As shown in FIGS. and 5A, instead of the row of point corona sources 68 a line corona source such as a corona wire 70 can be used as the source of the ion stream directed through the apertures "65 of the line modulator 61. A variety of related multilayered apertured line or bar modulators applicable for a use in the present invention are set forth in the US. Pat. application, Ser. No. 864,022 referred to above.

The main requirement for the toner material used in thesystem and method of the present invention is that the developed toner image be easily and efficiently transferrable to plain paper using conducted heat as described above. Conventional dry xerographic toner material can be used satisfactorily in a completely dry pro- 0.655 in the systems described above, for example, Sun Chemical Corporation Excello toner with a cascade type of development; Addressograph-multigraph Corporation Bruning 2000 toner with a magnetic brush type of developmentyor Sun Chemical Corporation R 415-64 used with a powder cloud type of development. In the completely dry embodiment of the process the dry toner materials are deposited on the transfer drum according to the latent charge imagine configuration. The remainder of the process, comprising transfer and fusing to print receiving means, drum cleaning, and drum discharging is the same as previously described. in the preferred form however the present invention contemplates a unique toner marking material comprising toner marking materials suspended in a liquid carrier in order to obtain benefits of liquid toner systems. r

The present invention particularly contemplates the use of a novel liquid toner suspension for efficient application in the heating and contact transfer methods and systems described above. ln conventional liquid electrophoretic toners, pigment particles such as carbon black are suspended directly in a liquid carrier along with resin or other polymer particles. The pigment material is generally suspended in the liquid carrier and becomes deposited in particulate form upon evaporation of the liquid after deposition. The piegment particles because of their yery small particle size adhere tenaciously to the dielectric transfer plate and are therefore diflicult to transfer with heat. Furthermore because of the low ratio of polymer resin material to pigment material the conventional liquid toner is relatively unaffected by the application of heat. Furthermore, while contact electrostatic transfer of the conventional liquid toner image is possible and has been done, it is subject to the disadvantages of having to contact the paper against wet solvent and solvent vaporization which are avoided by the present invention.

met. A relatively high resin or polymer binder content is provided in the particle material with the resin or polymer content being in the range of approximately -95 percent by weight while the pigment or colorant material content is inthe range of approximately 5-50 percent weight.

The particle size should fall in a range from 1 micron to 30 microns in order to permit effective and efficient transfer of particles from the dielectric transfer surface to the print receiving medium. This provides significantly increased transfer capability over conventional liquid toners in which the particle size is typically less than 0.1 micron diameter. While the preferred average particle size is in therange from 1 micron to 30 microns, the particle size distribution can be either narrow (mono-dispersed) or wide (poly-dispersed).

The resin or polymer material can be selected with a melting point considerably lower than the 300-350F melting point of conventional dry toners. Thus a melting point as low as 150F can be selected. Because of the low melting point heat fixing and contact transfer can be effected 'at higher speed and at lower temperatures with lower'energy and power or requirements. in conventional xerographic equipment using dry toner particles such a low melting point will result in agglomeration, aggregation and degradation of the dry toner particles during handling by'the mechanical handling equipment. Because there is no mechanical handling of dry toners in the present invention the low melting point resin matrix material is used in the liquid toner suspension without such problems.

ln addition to the binder of thermoplastic material containing pigment or other colorant material the particles may also contain charge control chemicals such as, for example 3, S-calcium di-isopropyl salicylate, Versamid 930, or linseed oil.

The dry toner particles are suspended in a nonconductive liquid having a resistivity when pure greater than approximately 10 ohm-centimeters. For example, a suitable aliphatic hydrocarbon fluid or fluorocarbon liquid can be used. The composition of the liquid toner suspension is adjusted so that the particles constitute approximately 0.01 percent to 10 percent by weight of the suspension and preferably in the range of 0.5-5 percent. The limitation on the range of relative composition of the suspension as between the particles and liquid carrier at lower concentrations is the length of time to adequately tone the image while at higher- .concentrations of particles the limiting factor is the build-up of dark background in the resultant image.

Other liquid toner suspension marking material arrangements in accordance with the present invention are contemplated. Instead of toner particles of the composition described above, latex-type toner'particles can be suspended in the carrier fluid or liquid. In order to prepare such a marking material a conventional latex polymer material-such as spheres of acrylic plastic of selected color suspended in water is used. The latex polymer material is subjected to hydrocarbon inversion in which the water is removed and the spheres of acrylic plastic suspended in hydrocarbon fluid. Charge control agents such as Versamid 930 are added so that the particles assume desired electrostatic charges. The plastic material of the particles is selected to' have a glass transition temperature to provide desired effects. For example, the glass transition temperature may be selected to be somewhat above or slightly above room temperature. At room temperature the plastic particles are glass-like and solid. The glass-like particles sus-. pended in the hydrocarbon fluid are applied to the latent charge image on the transfer drum, subjected to the air knife or air jet, and transferred to the paper or other print receiving medium under heat and pressure applied by the roller is heretofore described. With a glass transition temperature slightly above room temperature heating and power requirements for the roller are minimized. Upon melting and becoming plastic the plastic particle material soaks into the paper and upon exposure to the air undergoes curing and cross-linking.

Alternatively, with the glass transition temperature selected below room temperature the spheres of acrylic plastic or other suitable plastic material are in fluid plastic form, forming liquid or fluid droplets suspended in the hydrocarbon carrier. The liquid toner suspension marking material is thus effectively a liquid emulsion toner. The fluid droplets are independently and selectively charged by charge control agents so that they adhere to the latent charge image while the hydrocarbon fluid carrier is blown off by the air knife or air jet. Heating by the roller is thereby-effectively eliminated in the transfer step and the plastic material cures and undergoes cross-linking upon exposure to the air.

Other plastic materials in addition to acrylic plastics can be used for the suspended spheres such as styrenes and epoxies.

According to another embodiment the suspended particles in the carrier fluid comprises capsule particles of encapsulated liquid marking material which is released and fixed to the paper or other print receiving medium by the pressure roller. The pressure roller can be used in that event for applying pressure only, or

pressure and low heat.

Thus as used herein and in the following claims, the word particle alone is intended to encompass solid particles, essentially liquid droplets and capsules.

What is claimed is:

l. A system for electrostatic printing comprising:

a transfer medium formed with an insulative surface;

means for establishing an electrostatic latent image on the insulative of said transfer medium;

meansfor developing the electrostatic latent image on the transfer medium with a liquid toner;

means for dry-ing the toner on the transfer medium;

and means for effecting transfer of the developed image from the transfer medium to-a print receiving medium comprising means for pressure biasing a print receiving medium against the surface of the transfer medium and means for heating the print receiving medium and developed image whereby the toner is melted andfixed to the print receiving medium.

2. The system of claim 1 wherein said means for drying the toner on the medium comprises an air knife and means for supplying said air knife with air substantially saturated with vapors of the liquid toner vehicle.

3. A system for electrostatic printing comprising:

a transfer plate formed with an insulative surface;

. means for establishing a charge configuration on the insulative surface of thetransfer plate;

means for applying to the charge configuration on the transfer plate a liquid toner marking material comprising, toner particles suspended in a nonconductive liquid;

means for removing the liquid leaving toner particles retained against the transfer medium in the charge configuration;

means for applying a print receiving medium under pressure against the transfer plate;

and means for heating the print receiving medium and deposited toner particles during pressure contact whereby the toner particles are melted and fixed to the print receiving medium in the charge configuration.

4. The system of claim 3 wherein said means for removing the liquid comprises a jet of air substantially saturated with vapors of the liquid toner vehicle.

5. A system for electrostatic printing comprising:-

a transfer drum formed with an insulative outer surface and means for rotating said drum;

an imaging station for establishing on the surface of the drum an electrostatic latent image during rotation of the drum;

a developing station for applying to an electrostatic latent image formed on the surface of the drum a liquid toner suspension marking material comprising toner marking particles suspended in a nonconductive carrier liquid;

means for removing carrier liquid from liquid toner suspension marking material deposited on the transfer drum surface thereby leaving toner particles on the drum surface in the charge configuration of the electrosatic latent image;

a roller formed with a surface of elastomeric material positioned adjacent the transfer drum;

means for feeding a print receiving medium between the roller and transfer drum during rotation of the transfer drum;

means for compressing the roller against the surface of the drum and means for heating the roller, whereby the deposited toner on the transfer drum is melted and fixed to'the transfer medium in the conf guration of the electrostatic latent image.

6. The system of claim 5 wherein said means for removing carrier liquid comprises an air knife.

7. The system of claim 5 wherein said means for removing carrier liquid comprises means for physically separating said carrier liquid from said toner particles.

8. The systemof claim 5 wherein said means for removing carrier liquid comprises a substance which is substantially non-absorptive relative to said carrier liquid and means for thrusting said non-absorptive substance against said carrier liquid on said transfer drum.

9. The system of claim 8 wherein said non-absorptive substance is air substantially saturated with vapors of the liquid toner vehicle and wherein said means for thrusting said non-absorptive substance against said carrier liquid is an air knife.

l0. A system for electrostatic printing as set forth in claim 5, wherein the means for removing the liquid from liquid toner suspension applied to the transfer drum surface comprises an air knife for blowing off the liquid while the suspended toner particles are electrostatically retained against the surface of the drum.

11. A system for electrostatic printing as set forth in claim 5, wherein the means for removing the liquid from liquid toner suspension applied to the transfer drum surface comprises an absorbent roller.

drum after transfer of a'developed image from the drum surface to a print receiving medium and means for removing any latent charge remaining on the insulative drum surface whereby' the drum surface is prepared for receiving and developing another electrostatic latent image.

13. A system for electrostatic printing as set forth in claim 5,- wherein the imaging station for establishing on the surface of the transfer drum an electrostatic latent image comprises:

a multilayered apertured screen including at least an insulative layer and a conductive layer;

means for establishing across the face of the screen a. double'layer charge electrostatic latent image providing internal'fringing fields within the apertures of the screen of selected orientations and strengths for selectively blocking and enhancing a flow of charge particles directed through the apertures and for selectively controlling the flowof charge particles over a continuous range in accordance with the electrostatic latent image;

means for transporting said screen in synchronism with the transfer surface; and means for directing a line stream of charged particles through the screen in the direction of the transfer drum surface whereby the cross-section flow density of the charged particle stream is modulated in accordance with the configuration of charges on the screen and-whereby the particle 7 flow is deposited onthe transfer drum surface to form an electrostatic latent image of the desired configuration.

14. The system for electrostatic printing as set forth in claim 5, wherein the imaging station for establishingon the surface of the transfer drum an electrostatic la tent image comprises:

a multilayered aperture modulator comprising a layer of insulative material having a continuous conductive layer formed on one side thereof and a segmerited conductive layer formed onthe other side, with at least one row of apertures formed through the bar so that each segment of the segmented conductive layer substantially surrounds one of the apertures and so that each aperture is separately electrically addressable through the conductive segments, said multilayered apertured modulator positioned adjacent the surface of the drum and parallel with the drum rotationaxis;

means for applying separate selected electrical potential signals to the segments of the segmented conductive layer and means for applying a selected fixed potential to the continuous conducti've layer;

and means for directing a line stream of charged particles through the'modulator in the direction of the transfer drum surface whereby the cross-sectional flow. density of the charged particle stream is modulated in accordance with the potentials applied to the segments ofthe segmented conductive layer so that the particle flow is deposited on the transfer drum surface to form an electrostatic charged image of the desired configuration.

15. A system for electrostatic printing comprising:

atransfer medium formed with an insulative outer surface;

an imaging station for establishing on the surface of the transfer medium, an electrostatic latent image, said imaging station comprising a multilayered apertured element including at least an insulative layer and a conductive layer, means for establishing across the apertures, of the element double layer charges providing internal fringing fields within the aperture of the screen of selected orientations and strengths for selectively blocking and enhancing a flow of charged particles directed through theapertures and for'selectively controlling the flow of charge particles over a continuous range in accordance with the charge potentials, means for placing said element in juxtaposition with the transfer medium surface, and means for directing a stream of charged particles through the apertures of the element in the direction of the transfer medium surface whereby the cross sectional flow density of the charged particle stream is modulated in accordance with'the configuration of charges across the apertures of the element whereby the particle flow is deposited on the transfer medium surface to form an electrostatic latent image of the desired configuration;

a developing station for applying to an electrostatic latent image formed on thesurface of the transfer medium a liquid toner suspension marking material comprising toner marking particles suspended in a liquid;

means for removing liquid from liquid toner suspension deposited on the transfer medium surface thereby leaving toner particles on the transfer medium surface in the charge configuration of the electrostatic latent image;

a roller formed with a surface of elastomeric material positioned adjacent the transfer medium; I means for feeding a print receiving medium between the roller and transfer medium;

means for compressing the roller against the surface of the transfer medium and means for heating the roller, whereby the deposited toner on the transfer medium surface is melted and fixed to a print re ceiving medium in the configuration of the electrostatic latent image.

16. A system for electrostatic printing as set forth in claim 15, wherein the multilayered aperture element comprises a screen including a conductive layer and a photoconductive insulative layer, and wherein is provided means for establishing across the face of the screen a double layered charge electrostatic latent image comprising means for depositing a substantially uniform charge across the photoconductive insulative layers, means for applying voltage biases to the conductive layer, and means for projecting an image. to be reproduced onto the photoconductive insulating layer.

17. in a system for electrostatic printing, the combifusing means for simultaneously applying heat and pressure to paper at said printing station while said paper is contact applied to said developed image on said transfer medium. W

18. In a system for electrostatic printing, the combination comprising:

a transfer medium formed with a hard, durable, photoinert insulative outer surface;

imaging means including a multi-layered apertured element having at least an insulative layer and a conductive layer, means for providing layers of charge on opposed surfaces of said insulative layer for establishing fringing fields of selected strengths within the apertures of said element, and means for directing a stream of ions through said apertures in the direction of said transfer medium whereby said ion stream is modulated by said fringing fields to form an electrostatic latent image on said outer surface of said transfer medium;

developing means for applying toner marking particles to said electrostatic latent image on said transfer medium to develop such image; printing means for contact applying a sheet of paper or the like to the developed image on said transfer and fusing means for simultaneously applying heat andpressure to paper at said printing station while contact applied to said developed image on said transfer medium.

19. The combination recited in claim 18 wherein said developing means includes means for applying toner fluid to said electrostatic latent image.

20. The combination recited in claim 19 wherein said toner fluid is comprised of solid toner marking particles in a carrier fluid.

21. The combination recited in claim 19 wherein said carrier fluid consists of a non-conductive liquid.

22. The combination recited in claim 21 further comprising means for removing said liquid carrier fluid from said developed image before paper is applied thereto by said printing means. I

23. The combination recited in claim 22 wherein said liquid removing means comprises a substance-which is substantially non-absorptive relative to said liquid carrier fluid and means for thrusting said non-absorptive substance against said carrier liquid on said transfer medium to separate said liquid from said toner particles.

g 24. The combination recited in claim 23 wherein said non-absorptive substance is a gaseous substance substantially saturated with vapors of the liquid toner vehicle and wherein said thwsting means is a jet.

25. The combination recited in claim 23 wherein said non-absorptive substance is substantially saturated air and wherein said thrusting means is an air knife.

26. The combination recited in claim 22 wherein said liquid removal means removes said carrier liquid from said developed'image without appreciable evaporation.

27. The combination recited in claim 22 wherein said carrier liquid is substantially non-volatile.

28. The combination recited in claim 18 wherein said fusing means includes a heated roller having a deform able surface and means for biasing said roller against paper on said transfer medium.

29. The combination recited in claim 18 wherein said fusing means includes a heated roller having a deformable surface and means for biasing said roller against paper on said transfer medium.

30. The combination recited in claim 19 wherein said fusing means includes a heated roller having a deformable surface and means for biasing said roller against paper on'said transfer medium.

31. The combination recited in claim 20 wherein said fusing meansincludes a heated roller having a deformable surface and meansfor biasing said roller against paper on said transfer medium.

32. The combination recited in claim 21 wherein said fusing means includes a heated roller having a deformable surface and means for biasing said roller against paper on said transfer medium.

33. The combination recited in claim 22 wherein said fusing means includes a heated roller having a deformable surface and means for biasing said roller against paper on said transfer medium.

34. The combination recited in claim 23 wherein said fusing means includes a heated roller having a deformable surface and means for biasing said roller against paper on said transfer medium.

35. The combination recited in claim 24 wherein said I fusing means includes a heated roller having a deformable surface and means for biasing said roller against paper on said transfer medium.

36. The combination recited in claim 25 wherein said fusing means includes a heated roller having a deformable surface and means for biasing said roller against paper on said transfer medium.

37. The combination recited in claim 26 wherein said fusing means includes a heated roller having a deformable surface and means for biasing said roller against paper on said transfer medium. I

38. The combination recited in claim 27 wherein said fusing means includes a heated roller having a deformable surface and means for biasing said roller against paper on said transfer medium. 

2. The system of claim 1 wherein said means for drying the toner on the medium comprises an air knife and means for supplying said air knife with air substantially saturated with vapors of the liquid toner vehicle.
 3. A system for electrostatic printing comprising: a transfer plate formed with an insulative surface; means for establishing a charge configuration on the insulative surface of the transfer plate; means for applying to the charge configuration on the transfer plate a Liquid toner marking material comprising toner particles suspended in a non-conductive liquid; means for removing the liquid leaving toner particles retained against the transfer medium in the charge configuration; means for applying a print receiving medium under pressure against the transfer plate; and means for heating the print receiving medium and deposited toner particles during pressure contact whereby the toner particles are melted and fixed to the print receiving medium in the charge configuration.
 4. The system of claim 3 wherein said means for removing the liquid comprises a jet of air substantially saturated with vapors of the liquid toner vehicle.
 5. A system for electrostatic printing comprising: a transfer drum formed with an insulative outer surface and means for rotating said drum; an imaging station for establishing on the surface of the drum an electrostatic latent image during rotation of the drum; a developing station for applying to an electrostatic latent image formed on the surface of the drum a liquid toner suspension marking material comprising toner marking particles suspended in a non-conductive carrier liquid; means for removing carrier liquid from liquid toner suspension marking material deposited on the transfer drum surface thereby leaving toner particles on the drum surface in the charge configuration of the electrosatic latent image; a roller formed with a surface of elastomeric material positioned adjacent the transfer drum; means for feeding a print receiving medium between the roller and transfer drum during rotation of the transfer drum; means for compressing the roller against the surface of the drum and means for heating the roller, whereby the deposited toner on the transfer drum is melted and fixed to the transfer medium in the configuration of the electrostatic latent image.
 6. The system of claim 5 wherein said means for removing carrier liquid comprises an air knife.
 7. The system of claim 5 wherein said means for removing carrier liquid comprises means for physically separating said carrier liquid from said toner particles.
 8. The system of claim 5 wherein said means for removing carrier liquid comprises a substance which is substantially non-absorptive relative to said carrier liquid and means for thrusting said non-absorptive substance against said carrier liquid on said transfer drum.
 9. The system of claim 8 wherein said non-absorptive substance is air substantially saturated with vapors of the liquid toner vehicle and wherein said means for thrusting said non-absorptive substance against said carrier liquid is an air knife.
 10. A system for electrostatic printing as set forth in claim 5, wherein the means for removing the liquid from liquid toner suspension applied to the transfer drum surface comprises an air knife for blowing off the liquid while the suspended toner particles are electrostatically retained against the surface of the drum.
 11. A system for electrostatic printing as set forth in claim 5, wherein the means for removing the liquid from liquid toner suspension applied to the transfer drum surface comprises an absorbent roller.
 12. A system of electrostatic printing as set forth in claim 5, wherein is provided means for cleaning the drum after transfer of a developed image from the drum surface to a print receiving medium and means for removing any latent charge remaining on the insulative drum surface whereby the drum surface is prepared for receiving and developing another electrostatic latent image.
 13. A system for electrostatic printing as set forth in claim 5, wherein the imaging station for establishing on the surface of the transfer drum an electrostatic latent image comprises: a multilayered apertured screen including at least an insulative layer and a conductive layer; means for establishing across the face of the screen a double layer charge electrostatic latent image providing internal fringing fields witHin the apertures of the screen of selected orientations and strengths for selectively blocking and enhancing a flow of charge particles directed through the apertures and for selectively controlling the flow of charge particles over a continuous range in accordance with the electrostatic latent image; means for transporting said screen in synchronism with the transfer surface; and means for directing a line stream of charged particles through the screen in the direction of the transfer drum surface whereby the cross-section flow density of the charged particle stream is modulated in accordance with the configuration of charges on the screen and whereby the particle flow is deposited on the transfer drum surface to form an electrostatic latent image of the desired configuration.
 14. The system for electrostatic printing as set forth in claim 5, wherein the imaging station for establishing on the surface of the transfer drum an electrostatic latent image comprises: a multilayered aperture modulator comprising a layer of insulative material having a continuous conductive layer formed on one side thereof and a segmented conductive layer formed on the other side, with at least one row of apertures formed through the bar so that each segment of the segmented conductive layer substantially surrounds one of the apertures and so that each aperture is separately electrically addressable through the conductive segments, said multilayered apertured modulator positioned adjacent the surface of the drum and parallel with the drum rotation axis; means for applying separate selected electrical potential signals to the segments of the segmented conductive layer and means for applying a selected fixed potential to the continuous conductive layer; and means for directing a line stream of charged particles through the modulator in the direction of the transfer drum surface whereby the cross-sectional flow density of the charged particle stream is modulated in accordance with the potentials applied to the segments of the segmented conductive layer so that the particle flow is deposited on the transfer drum surface to form an electrostatic charged image of the desired configuration.
 15. A system for electrostatic printing comprising: a transfer medium formed with an insulative outer surface; an imaging station for establishing on the surface of the transfer medium, an electrostatic latent image, said imaging station comprising a multilayered apertured element including at least an insulative layer and a conductive layer, means for establishing across the apertures of the element double layer charges providing internal fringing fields within the aperture of the screen of selected orientations and strengths for selectively blocking and enhancing a flow of charged particles directed through the apertures and for selectively controlling the flow of charge particles over a continuous range in accordance with the charge potentials, means for placing said element in juxtaposition with the transfer medium surface, and means for directing a stream of charged particles through the apertures of the element in the direction of the transfer medium surface whereby the cross-sectional flow density of the charged particle stream is modulated in accordance with the configuration of charges across the apertures of the element whereby the particle flow is deposited on the transfer medium surface to form an electrostatic latent image of the desired configuration; a developing station for applying to an electrostatic latent image formed on the surface of the transfer medium a liquid toner suspension marking material comprising toner marking particles suspended in a liquid; means for removing liquid from liquid toner suspension deposited on the transfer medium surface thereby leaving toner particles on the transfer medium surface in the charge configuration of the electrostatic latent image; a roller formed with a surface of elastomeric material positioned adjacEnt the transfer medium; means for feeding a print receiving medium between the roller and transfer medium; means for compressing the roller against the surface of the transfer medium and means for heating the roller, whereby the deposited toner on the transfer medium surface is melted and fixed to a print receiving medium in the configuration of the electrostatic latent image.
 16. A system for electrostatic printing as set forth in claim 15, wherein the multilayered aperture element comprises a screen including a conductive layer and a photoconductive insulative layer, and wherein is provided means for establishing across the face of the screen a double layered charge electrostatic latent image comprising means for depositing a substantially uniform charge across the photoconductive insulative layers, means for applying voltage biases to the conductive layer, and means for projecting an image to be reproduced onto the photoconductive insulating layer.
 17. In a system for electrostatic printing, the combination comprising: a transfer medium formed with a hard durable photo-inert insulative outer surface; imaging means for establishing an electrostatic latent image on the surface of said transfer medium; developing means for applying toner marking particles to said electrostatic latent image on said transfer medium to develop such image; printing means for contact applying a sheet of paper or the like to the developed image on said transfer medium; and fusing means for simultaneously applying heat and pressure to paper at said printing station while said paper is contact applied to said developed image on said transfer medium.
 18. In a system for electrostatic printing, the combination comprising: a transfer medium formed with a hard, durable, photoinert insulative outer surface; imaging means including a multi-layered apertured element having at least an insulative layer and a conductive layer, means for providing layers of charge on opposed surfaces of said insulative layer for establishing fringing fields of selected strengths within the apertures of said element, and means for directing a stream of ions through said apertures in the direction of said transfer medium whereby said ion stream is modulated by said fringing fields to form an electrostatic latent image on said outer surface of said transfer medium; developing means for applying toner marking particles to said electrostatic latent image on said transfer medium to develop such image; printing means for contact applying a sheet of paper or the like to the developed image on said transfer medium; and fusing means for simultaneously applying heat and pressure to paper at said printing station while contact applied to said developed image on said transfer medium.
 19. The combination recited in claim 18 wherein said developing means includes means for applying toner fluid to said electrostatic latent image.
 20. The combination recited in claim 19 wherein said toner fluid is comprised of solid toner marking particles in a carrier fluid.
 21. The combination recited in claim 19 wherein said carrier fluid consists of a non-conductive liquid.
 22. The combination recited in claim 21 further comprising means for removing said liquid carrier fluid from said developed image before paper is applied thereto by said printing means.
 23. The combination recited in claim 22 wherein said liquid removing means comprises a substance which is substantially non-absorptive relative to said liquid carrier fluid and means for thrusting said non-absorptive substance against said carrier liquid on said transfer medium to separate said liquid from said toner particles.
 24. The combination recited in claim 23 wherein said non-absorptive substance is a gaseous substance substantially saturated with vapors of the liquid toner vehicle and wherein said thrusting means is a jet.
 25. The combination recited in claim 23 wherein said non-absorPtive substance is substantially saturated air and wherein said thrusting means is an air knife.
 26. The combination recited in claim 22 wherein said liquid removal means removes said carrier liquid from said developed image without appreciable evaporation.
 27. The combination recited in claim 22 wherein said carrier liquid is substantially non-volatile.
 28. The combination recited in claim 18 wherein said fusing means includes a heated roller having a deformable surface and means for biasing said roller against paper on said transfer medium.
 29. The combination recited in claim 18 wherein said fusing means includes a heated roller having a deformable surface and means for biasing said roller against paper on said transfer medium.
 30. The combination recited in claim 19 wherein said fusing means includes a heated roller having a deformable surface and means for biasing said roller against paper on said transfer medium.
 31. The combination recited in claim 20 wherein said fusing means includes a heated roller having a deformable surface and means for biasing said roller against paper on said transfer medium.
 32. The combination recited in claim 21 wherein said fusing means includes a heated roller having a deformable surface and means for biasing said roller against paper on said transfer medium.
 33. The combination recited in claim 22 wherein said fusing means includes a heated roller having a deformable surface and means for biasing said roller against paper on said transfer medium.
 34. The combination recited in claim 23 wherein said fusing means includes a heated roller having a deformable surface and means for biasing said roller against paper on said transfer medium.
 35. The combination recited in claim 24 wherein said fusing means includes a heated roller having a deformable surface and means for biasing said roller against paper on said transfer medium.
 36. The combination recited in claim 25 wherein said fusing means includes a heated roller having a deformable surface and means for biasing said roller against paper on said transfer medium.
 37. The combination recited in claim 26 wherein said fusing means includes a heated roller having a deformable surface and means for biasing said roller against paper on said transfer medium.
 38. The combination recited in claim 27 wherein said fusing means includes a heated roller having a deformable surface and means for biasing said roller against paper on said transfer medium. 